1. Field of the Invention
The present invention relates to a semiconductor device including MISFET in which silicide to be Schottky junctioned to a silicon substrate is used in source and drain, and a method for manufacturing the semiconductor device.
2. Description of the Related Art
A process (replacement gate process, damascene gate process) using a dummy gate has been proposed in order to apply a metal gate and highly dielectric gate insulating film to MOSFET (reference documents: A. Chatterjee et al., IEDM Tech. Dig., (1997), p. 821 and A. Yagishita et al., IEDM Tech Dig., (1998), p. 785).
Here, the dummy gate process comprises: forming a disposable gate to be removed later in a region forming a gate in future; forming a source/drain in the region by self-alignment; removing the dummy gate; and using a damascene process in a trench formed by removing the dummy gate to replace the dummy gate with an intrinsic gate.
When the dummy gate process is used, the source/drain requiring a high-temperature thermal treatment is formed before the gate. Therefore, a thermal process after gate formation can be performed at a low temperature of 450° C. or less. Therefore, it is easy to apply a metal gate electrode or a highly dielectric gate insulating film inferior in heat resistance to MISFET.
Problems of a damascene gate (or a replacement gate) transistor using a metal gate and high-k gate insulating film are as follows:
(1) a number of process steps remarkably increases in order to form and remove the dummy gate;
(2) a short channel effect is deteriorated by a fringe (exudation) effect of a gate electric field (reference document: Baohong Cheng et al., IEEE Transactions on ELECTRON DEVICES, Vol. 46, No. 7, (1999), p. 1537); and
(3) work functions of many metal gates for use are positioned in the vicinity of a mid gap of silicon, and this influences/increases a threshold voltage (absolute value).